Electric valve circuit



Oct. 5, 1943. c. E. SMITH ELECTRIC VAI-LVB CIRCUIT Filed May l0, 1941MSB mvENToR {f4/de f. 5/22/777. BY

WITN ESSES:

ATTORNEY Patented Oct. 5, 1943 ELEUIRIC VALVE lCIRJCUIT Clyde E. Smith,Wilkinsburg, Pa., assignor to Westinghouse Electric & ManufacturingCompany, East Pittsburgh, Pa., a corporation of PennsylvaniayApplication May 10, 1941, Serial N0. 392,869

(ci. zsogzv) 6 Claims.

My invention relates to electric discharge valve circuits, and hasparticular relation to circuits employed for controlling the supply ofenergy to a load.

In using apparatus with electric discharge valves connected between asource of potential anda load, it becomes desirable for certainoperations to alter the amount of energy supplied through the valves;The necessity for equipment of simple and inexpensive structure toetl'ect the change is particularly urgent in cases in which valvecircuits are used for supplying direct current to a load from a sourceof periodically pulsating potential; for example, in welding apparatusof the magnetic storage energy type such as is disclosed in thecopending application of Donald P. Faulk, Serial No. 374,662, iiledJanuary 16, 1941, Patent No. 2,300,538, and assigned to the WestinghouseElectric 8l Manufacturing Company. In this case the electric dischargevalve means is interposed betweena source of periodically pulsatingpotential and the highly reactive primary of the welding transformer toimpress a potential on the latter for supplying.l

charging current therethrough. After the reactor is charged, the supplycurrent is interrupted permitting the reactor to discharge. The decay influx in the welding transformer as the reactor discharges, induces apotential in the secondary causing welding current to `ilow through theelectrodes connected thereto. v

The apparatus is used primarily in welding stainless steel or aluminumand in making other high quality welds, and the values are normallyarranged to impress the maximum available potential on the weldingtransformer. However, in the welding of certain materials, such as thingauge aluminum, it is necessary to decrease the potential impressed uponthe Welding transformer from the normal value to obtain uniformity inthe quality of the weld. With a low impressed potential, the chargingcurrent rises slowly so that any slight delay in interruption does noteffect the character of the weld of the thin sheets.

The necessary low potential is achieved in accordance with the teachingof the prior art of which I am aware by varying the supply transformeroutput. However, this expedient is often inconvenient and frequentlyinvolves comparatively expensive equipment.

VIt is accordingly an object of'my invention tov providev anelectricdischarge valve circuit including simple and inexpensive means foraltering the amount of energy which is supplied through the valve means.

Another object of my invention is to provide an electric. dischargevalve rectifier with novel means for changing the value of the potentialsupplied therefrom at will.

A further object of my invention is to provide a novel electricdischarge valve circuit for supplying a direct current to a load from asource of periodically pulsating potential in which the amount of energysupplied may be altered at will.

A more speciic object of my invention is to provide a welding system ofthe magnetic storage energy type in which the magnitude of the weldingcurrent shall be precisely adaptable to the gauge of the materialwelded.

Another specific object of my invention is to provide a simple andtractable welding system of the magnetic storage energy type which shallhave a plurality of distinct current settings for welding materials ofdifferent gauge.

My invention arises from the realization that only two settings are inpractice necessary to render the welding apparatus suitable for weldingmaterials over a wide range of thickness. One setting is used for thickmaterials and the other for thin materials.

In accordance with my invention, the energy supplied to a load or thewelding material through electric discharge valve means is altered atwill by a switching device which interposes a iixed time delay elementin the control circuit of each supply valve or removes the element fromthe control circuit. The control circuit of each supply valve includesan auxiliary electric discharge device so connected that both the deviceand the associated supply valve are in condition to become conductiveduring the same potential pulsations. Control means are provided toestablisha voltage between the control electrode and cathode of eachauxiliary device of a valve such that the device is rendered conductiveat aY predetermined time during individual potential pulsations. Firingcf the auxiliary device causesv the associated valve to be renderedconductive. Since the electric discharge valve means is of the type thatcontinues to conduct current throughout a potential pulsation once ithas been rendered conductive, the amount of energy supplied, or theaverage potential impressed on, the load depends upon the time duringthat pulsation at which the auxiliary device becomes conductive.

When it is necessary to reduce the potential impressed upon the load, atime delay means is inserted inthe control `circuit of each supplyvalve. The time delay means may take the form of a capacitor connectedat will across the control electrode and Cathode of each auxiliarydevice. The capacitor has its negative plate connected to the controlelectrode and, therefore, its potential must be overcome before thenecessary positive control electrode-cathode potential n may beestablished to eifect iiring of the device.

The time required to. overcome 'the 'capacitor potential is determinedby the dimensions of the objects and advantages thereof, willbest beunderstood from the following description of a specific embodiment whenread in connection` with the accompanying drawing, in which:

Figure 1 is a diagrammaticview of a weldin apparatus embodying myinvention, y

l Fig. 2 is a graph illustrating the maximum available potentialimpressed on theV load, and

Fig. 3 is a graph -illustrating the potential impressed on the loadafter the time delay means has been inserted in the control circuit. l

The apparatus shown in Fig. 1 is similar to that disclosed and describedin the aforementioned copending application of Donald P. Faulk. A supplytransformer 5 is energized from a source oi polyphase potential 1, thetransformer secondary 9 being connected in zigzag. Electric dis-- chargevalves li, I3 and l5 of the arc-'like type, preferably ignitrons, areconnected between the external terminals of the secondary 9 of thesupply transformer 5 and the primary H ofV -the welding transformer I9.Each of the supply igni-` trons H, I3 andri is provided with a controlVcircuit including an auxiliary discharge device- 2| which may be athyratron with its anode 23 and cathode connected to the anode 21 andigniter 2Q of the corresponding ignitron through the contacter 3l of acontrol relay 33 and a current limiting resistor 34. A potential isestablished between the control electrode or grid and the cathode 25 ofeach thyratron 2l by av circuit including a resistor 37 connected acrossthe anode and gridof the thyratron. The control voltage thus providedreaches a positive value such that each thyratron is red as itscorresponding phase potential exceeds the other phase potentials. Aseach thyratron is fired, the corresponding supply ignitron is renderedconductive to impress its phase potential across the primary of thewelding transformer for supplying charg- 1ol Thus ring of the device andconsef f thyratrons 2l for controlling the supply ignitrons. During thenegative half` cycle of the corresponding phase potential, the capacitor49 is charged with the plate connected to the control electrode 35 ofthe associated thyratron negative. The charging circuit of eachcapacitor 'Se can be traced from one side of the secondary 9 ofthesupply transformerthrough the primary I1 of the welding transformer, thecathode i i3 and igniter 29 of the corresponding ignitron, contactorlil, capacitor 19, grid resistor 3l, contactor 3l and resistor 34 to theother side of the secondary 9. Then during the positive half cycle ofthe corresponding phase potential, iiring of the corresponding thyratronis delayed because the charge on the capacitor AQ must be overcome andthe capacitorcharged in the opposite direction until the potentialbetween grid 35 and the cathode 25 of the corresponding thyratronreaches a positive value to render the thyratron conductive. The extentof the delay in the iiring of each thyratron depends therefore upon thedimensions of the vcapacitor 49 with respect to resistor 31. Thecapacitor is recharged in the original direction during the negativehalf cycle of the corresponding phase potential. With the capacitor 49connected in the control circuits, each thyratron 2l is red apredetermined time after its phase potential exceeds the other phasepotentials. Consequently, the average potential impressed across theprimary Il is reduced a predeterminedl amount. A

As thecharging current flows through the primaryl'l of .the weldingtransformer i9, it gradually increases because of the hihreactance ofthe primary. A current relay 5i is placed in series -with the primaryl,.and when the charging current reaches the desired value, the currentrelay 5| operates'to effect deenergization of the control relay 33. Thecontactors Si of the control relay open the anode circuits of eachthyratron 2i to prevent ring thereof. One of the supply ignitrons isconductive when the anode circuits of the thyratrons are opened. Thenonconductive ignitrons do not become conductive in successionthereafter, vbut the conductive ignitron continues to conduct current.and thev potential impressed on the primary decreases as thecorrespending phase potential of theconductive ignitron decreases. Thevariation in the impressed potential causes firing of another electricdischarge device 53 which is connected in series with a blockingcapacitor 55. As the discharge device 53 which is preferably anignitron, becomes conductive, the blocking capacitor 55 is connectedacross the` conductive supply ignitron. The blocking capacitor isoriginally'charged so that when connected across the conductive supplyignitron, it opposes Athe flow of current and renders the supplyignitron non-conductive.

The supply current is thus interrupted and the primary H yof the weldingtransformer is permitted to discharge through a shunting ignitron 57 anda variable resistor 59 connected in series therewith. The shuntingignitron 5i is rendered conductive by a control circuit responsive tothe potential across the primary li shortly after the supply current isinterrupted. The decay in ux in the welding-'transformer causesweldingcurrent to ow throughthe secondary 6I and the welding electrodes63 and 65 connected therewith.

With the apparatus in the condition lshown in Fig. 1, a weldingoperation may :be initiated by closing .a manual controllerv such as afoot switch S1. The lower movablecontactor S9 of the controller 81closes completing a circuit through the energizing coil 1I of a fluidpressure valve 13. The valve operates permitting a iluid under pressureto flow into a piston chamber 15 and to move a piston 11. The piston 11carries a movable welding electrode 63 and when it is actuated, themovable electrode is urged into engagement with the material 18 to bewelded which, in turn, is held in engagement with the fixed weldingelectrode 65. The fluid continues to flow increasing the pressure on thepiston 11 and exerting pressure on another piston 19 in an auxiliarychamber 8| in communication with the electrode piston chamber 15. Thelatter piston moves against the action of a spring 83 and closes themovable contactor 85 of a pressure switch 81 when the pressure on themovable welding electrode has reached the desired magnitude. i

The exciting coil 89 of the control relay 33 is now energized in acircuit extending from an upper terminal of the secondary 9| of theauxiliary source transformer 4| through the manual controller, contactor93, the pressure switch 81, the normally closed contactor 95 of a secondauxiliary relay 91, the exciting coil 89 of the control relay 33 to thelower terminal of the secondary 9|. The control relay is thus energizedand its contactors 3| close the anode circuits of the thyratrons 2|controlling the supply ignitrons. Control relay 33 has two additionalcontactors 99 and II. Contactor 99 closes a circuit in a full waverectifier |03 for charging the blocking capacitor 55 and contacter IOIplaces a capacitor across the grid I01 and cathode |99 of a thyratronIII which controls ring of the ignitron 53 in series with the blockingcapacitor 55.

As the phase potential applied to each of the firing thyratrons 2| forthe supply ignitrons I I through I5 exceeds the other phase potentials,the thyratron is rendered conductive. Firing current for thecorresponding ignitron then flows from a terminal of the supplyktransformer secondary 9 through contacts 3|, the thyratron 2|, theigniter 29 and the cathode I I3 of the ignitron, the primary I1 of thewelding transformer I9 to the other terminal of the secondary i9. Thesupply ig'nitrons are thus rendered conductive in succession andcharging current flows through the primary of the welding transformerand the eX- citing coil I|5 of the current relay 5|. When the chargingcurrent reaches a predetermined value, the current relay is energizedand its contactor I I1 closes.

A circuit is now completed which extends from the upper terminal of thesecondary 9| of the auxiliary transformer` 4I through contactor 93 ofthe manual controller l61, the exciting coi1 I I9 of the auxiliary relay91, the contactor I1 of the current relay 5| to the lower terminal ofthe secondary 9|. The auxiliary relay 91 closes its contactor I2| toestablish a holding circuit therefor and opens its normally closedcontactor 95 breaking the circuit through the exciting coil of thecontrol relay 33. As a result, the charging circuit of the blockingcapacitor 55 is broken, the capacitor |05 is disconnected from the gridand cathode of the thyratron III controlling the conductivity of theignitron 53 in series with the blocking capacitor 55, and the anodecircuits of the firing thyratrons 2| for the supply ignitrons areopened.

As the operation progresses, the non-conductive ignitrons II through I5do not become conductive in their turn because their firing thyratrons`2| are non-conductive. ,f The conductive ignitr'on continues to carrycurrent as the potential of the phase from which it is supplieddecreases, by reason of the reactive impedance in its anode-cathodecircuit. As the phase potential decreases, the potential across theprimary of the welding transformer correspondingly increases from itsnegative value and eventually the net potential attains such a valuethat it counteracts a biasing potential |23 in the control circuit ofthe thyratron III associated with the ignitron 53 in series with theblocking capacitor 55. The control circuit for the thyratron III extendsfrom its control electrode |01 through a grid resistor |25 to thebiasing potential |23, thence through the parallel network consisting ofa primary I1 of the welding transformer on one side and the windings ofthe supply secondary 9 on the other side, and finally through thecathode |21 and igniter |29 of the ignitron 53 to the cathode |09 of thethyratron III. When the bias potential |23 is counteracted and thecritical potential of the thyratron III exceeded, the thyratron is firedto render the ignitron 53 conductive. The blocking capacitor 55 isconnected across the supply ignitrons through a resistor I3I andforcibly deionizes the conductive ignitron.

The purpose of the capacitor |05 connected across the grid and cathodeof the firing thyratron II I for the ignitron connected in series withthe blocking capacitor 55 is to prevent the blocking capacitor frombeing connected across the supply ignitrons before the charging currentreaches its desired value. While the capacitor |95 is so connected, itis charged with its negative plate connected to the grid of thethyratron III by the supply voltage impressed across the circuitextending through the cathode |21 of the ignitron 53, the contacter IOIof the control relay 33, the capacitor I 05, the resistor |25 and 'biaspotential |23. If for any reason the biasing potential |23 iscounteracted before the predetermined supply current value is reached,the thyratron III is not rendered conductive. Instead the voltage isused to charge the capacitor |05 in the opposite direction. The size ofthe capacitor |95 is such that the time required to charge it from itsnegative Value to a positive value by the potential available, isgreater than the time necessary for the phase potential to continue itscycle and return to its former condition in which the biasing potentialis not counteracted. It is to be noted that when the firing of thesupply ignitrons is delayed, whether deliberately to reduce theimpressed potential or accidentally, the phase potential may decrease toa value equal to that used to effect firing of the thyratron I I I andan interruption of the supply of current. However, the interruption isprevented by the capacitor |05 in the control circuit of the thyratron.It is, therefore, necessary to disconnect the capacitor |05 from thecontrol circuit before an interruption can take place.

As the blocking capacitor 55 interrupts the charging current, the risingreactor potential is impressed across the principal electrodes of theshunting ignitron 51 and the firing thyratron |33 therefor. The shuntingignitron 51 is rendered conductive and the reactor I1 discharges throughthe shunting ignitron and a variable resistor 59 connected in seriestherewith. The

. decay in flux in the welding transformer I9 as the manual controller(il and reclosing it. When the controller is released, the holdingcircuitfor the auxiliary relay 97 opens resetting the apparatus.

In Fig. 2 is shown a series of curves i3d with potential plottedvertically and time horizontally. The curves are sine waves partiallyVbroken and partially in full line representing the phase potentialssupplied from the secondary 9 of the supply transformer 5. As each phasepotential exceeds the other phase potentials, as represented by thepoint T, the associated supply ignitron is rendered conductive toimpress the phase potential across the primary i7 of the weldingtransformer i9. The full line curve 37 made up of the top portions ofthe sine waves represents the potential impressed across the primary. Asthe average impressed potential is proportional to the area beneath theimpressed potential curve, it is obvious that the maximum availablepotential is impressed on the welding transformer.

In Fig. 3 is shown a graph with potential plotted vertically and timehorizontally in which the phase potentials are again represented by sinecurves l35. However, this graph illustrates the potentials impressed onthe welding transformer i9 when the time delay means is inserted in thecontrol circuits of the supply ingnitrons. Consequently, as each phasepotential exceeds the other phase potentials, the associated supplyignitron is not rendered conductive but its ring is delayed until somepredetermined later time as represented 'by the point T. The full linecurve Vil represents the potential impressed onV the weldingtransformer. Comparison of the areas beneath the impressed potentialcurves of Figs. 2 and 3 discloses that the average potential impressedwhen the time delay means is inserted in the control circuits is reduceda predetermined amount.

in a system in accordance with my invention which has actually beenconstructed and tested, the supply ignitrons Il, i3 and l5 areWestinghouse WIJ-656 tubes andare energized from a source through atransformer 5 to impress a potential of 130 volts D. C. on the reactori1. The iiring thyratrons 2l for the supply ignitrons are Westinghouse632 tubes and the resistors 34 in the anode circuits thereof are 2 ohms.The grid resistors 37 of the firing thyratrons 2l for the supplyigntrons are .5 megohm each. The capacitors t9 which are inserted across.the grid and cathode of the firing thyratrons 2l for the supplyignitrons are each .O05 microiarad and delay ring of the supplyignitrons to impress 88 volts on the welding transformer.

Although I have shown and described certain specific embodiments of myinvention, I am fully aware that many modifications thereof arepossible. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art and the spirit of theappended claims.

I claim as my invention: 1

l. For use in supplying a direct current to a load from a source ofpolyphase potential, the combination comprising electric discharge valvemeans connected between each phase of said source and said load t0impress a potential on the latter to supply current therethrough,control means for each of said valve means including an auxiliary.discharge device for controlling the conductivity of the correspondingvalve means and having an anode, a cathode and a controlelectrode,saidanode and cathode being 'connected to receive the correspondingphase potential thereacross, means for establishing a control po.-tential between said control electrode and cathode of .each device suchthat the device is rendered conductive at a rst predetermined timeduring each period of the corresponding phase potential, a plurality ofcapacitors, and a single means for connecting one of said capacitorsacross the control electrode and cathode of each device to prevent saidvdevice from being rendered conductive until a second predetermined timeduring each period of the corresponding phase potential. Y

2. In combination, a source of periodic potential, an electric dischargedevice of the arc-like type having a plurality of principal electrodesin circuit with said source Vand a control electrode, said device beingrendered conductive in a positive period of said source upon theestablishment of a potential greater than a predetermined criticalmagnitude between said control electrode and one of said principalelectrodes, means for impressing a periodic potential between saidcontrol electrode and one principal electrode which first rises abovesaid critical magnitude at a first preselected instant in each positiveperiod of said source, a capacitor, and means independent of saidpotential impressing means and operable at will for connecting saidcapacitor between said control electrode and one principal electrode toprevent said device from being rendered conductive until a second andlater preselected instant in each positive period.

3. In combination, a source of potential, an electric discharge deviceof the arc-like type having a plurality of principalelectrodes incircuit with said source and a control electrode, said device beingrendered conductive upon the establishment between said controlelectrode and one of said principal electrodes of a potential greaterthan a predetermined critical magnitude, means for impressing apotential across said control electrode and said one principal electrodewhich nrst rises above said critical value at a preselected time, acapacitor, and means independent of said potential impressing means andincluding a switch operable at will for connecting said capacitorbetween said control electrode and said one principal electrode toprevent said device from being rendered conductive until a secondpreselected time later than said first time.

4. In combination, a source of alternating potential, an electricdischarge device of the arc-like type having an anode and a cathode incircuit with said source and a control electrode, said device beingrendered conductive in a positive half period of said source when thepotential of said control electrode with respect to said cathode risesabove a predetermined critical value, resistance means interconnectingsaid control electrode and said anode whereby the potential of saidcontrol electrode with respect to said cathode rises above said criticalvalue at a preselected instant in each positive half period, a capacitorand means operable at will for connecting said capacitor between saidcontrol electrode and said cathode so that said capacitor and resistancemeans are in series across said anode and Vcathode to prevent thepotential of said control electrode with respect to said cathode fromrising above said critical value until a second and later preselectedinstant in each positive half period.

5. For use in supplying a direct current to a load from a source ofpolyphase potential, the combination comprising an electric dischargedevice for each phase of said source, each of said devices having aplurality of principal electrodes connected between the correspondingphase of the source and said load and a control electrode, each of saiddevices being rendered conductive upon the establishment of a potentialbetween said control electrode and one of said principal electrodeswhich is greater than a predetermined critical value during a positivehalf period of the corresponding phase potential, means for impressing apotential between said control electrode and one principal electrode ofeach of said devices which rst rises above said critical value at afirst preselected instant in the positive half period of thecorresponding phase potential, a capacitor for each of said devices, anda single means operable at will for connecting said capacitors betweenthe control electrode and said one principal electrode of thecorresponding device whereby to prevent said devices from being renderedconductive until a second and later preselected instant in each positivehalf period of the corresponding phase potential.

6. For use in supplying a direct current to a load from a source ofpolyphase potential, the combination comprising an electric dischargedevice for each phase of said source, each of said devices having ananode and cathode connected between the corresponding phase of thesource and said load and a control electrode, resistance meansinterconnecting the control electrode and the anode of each of saiddevices, a capacitor for each of said devices, and a single meansoperable at will for connecting said capacitors between the controlelectrode and the cathode of the corresponding devices whereby theamount of energy supplied to the load may be changed at will.

CLYDE E. SMITH.

